Anesthetic evaporators are used in conjunction with anesthesia apparatuses in order to enrich a carrier gas, usually a laughing gas-oxygen mixture or an air-oxygen mixture, with a volatile anesthetic. The anesthetic is filled in the liquid state into the evaporation chamber, which is equipped with a wick device, which is completely soaked with the anesthetic and releases the evaporating liquid anesthetic from its surface to the carrier gas flowing through the evaporation chamber. The wick device may be, e.g., a wick made of nonwoven felt or another nonwoven-like knit material, but it may also consist of a porous, absorbent body, e.g., sintered glass, which is in liquid contact with the anesthetic. The percentage of gaseous anesthetic in the carrier gas is usually a few volume percent. To set this percentage, and also to change it during the anesthesia as needed, a metering unit, which is adjustable via a handwheel, is located on the anesthetic evaporator. The majority of the carrier gas flow flows past the evaporation chamber in a bypass line. A small percentage of the carrier gas is led from a branch of the carrier gas into txe evaporation chamber, in which it is enriched with the anesthetic to saturation and is fed via an adjustable metering gap into the rest of the carrier gas flow in the bypass line A mixed gas, which contains a percentage of gaseous anesthetic adjustable by means of the metering unit, is thus obtained. The percentage of anesthetic in the mixed gas is changed by changing the width of the metering gap. The gaseous anesthetic of such a composition is led from a mixed gas outlet to an anesthesia apparatus, by which the gaseous anesthetic is fed to the patient to be treated.
Such an anesthetic evaporator is described in DE-25,07,261 A1 (U.S. Pat. No. 4,017,566). In this evaporator the anesthetic is contained as a filling in a pot-like evaporation chamber in the evaporator, and the impregnated wicks immerse into the liquid reserve.
Part of the carrier gas flows via an evaporation chamber line into the interior of the evaporation chamber, is enriched with the anesthetic gas at the wicks, leaves the evaporation chamber via a return line, and flows through the metering gap into the bypass line. The anesthetic gas is mixed there with the rest of the carrier gas and is led as a mixed gas to the mixed gas outlet. The evaporation of the anesthetic brings about a change in temperature in the area of the evaporation chamber (latent heat) as a function of the carrier gas flow, depending on the setting of the concentration by changing the width of the metering gap. If the setting of the metering gap, once set, which acts as a flow regulating valve, were left unchanged, the anesthetic concentration in the mixed gas would therefore change; it is reduced by cooling. The change in the ambient temperature also affects the metering. It is therefore also necessary to change the metering gap acting as a flow regulating valve, once set, depending on the change in temperature. A temperature compensation device, which changes the gap width and consequently the flow resistance of a flow regulating valve in the bypass line via a temperature-dependent change, is therefore provided in the prior-art anesthetic evaporator.
Since the liquid anesthetic reserve is stored in a reservoir of the evaporation chamber, it is necessary to operate the anesthetic evaporator in a certain preferred position in order to prevent liquid anesthetic from entering the flow channels, especially the flow regulating valves. The narrow metering gaps of the flow regulating valves and the lines in the bypass channel could retain liquid as a consequence of capillary forces, so that correct metering would no longer be possible. In addition, the lines carrying the carrier gas would be wetted with anesthetic, so that a concentration, once set, would not be maintained, because additional anesthetic would evaporate from the gascarrying lines in an uncontrollable manner, and it would be fed to the mixed gas outlet. While the position in the operating state of the anesthetic evaporator in the upright position can be ensured by technical means, e.g., by suitable measures on the anesthesia apparatus, oblique positions of the anesthetic evaporator may occur during the transportation of the anesthetic evaporator or even of the complete anesthesia apparatus (especially in the case of small, portable anesthesia apparatuses), or the anesthetic liquid may penetrate into gas-carrying lines, especially into the flow regulating valves, due to shaking during transportation. The possibility that the anesthetic evaporator will be in such an oblique position, in which liquid anesthetic will fill the gas-carrying flow channels in an undesired manner, also cannot be ruled out during the storage of a filled anesthetic evaporator, namely, especially during transportation from and to the place of storage. This circumstance is all the more significant as it is impossible to determine from an anesthetic evaporator standing upright in what position (lying, upright, or upside down) it has been since it was filled with anesthetic. To eliminate disadvantageous consequence of an undesired oblique position, it would be necessary to specify that the gas-carrying lines be rinsed, before an anesthetic evaporator is put into operation, until the concentration set on the handwheel is reached at the mixed gas outlet. This would lead to a delay in the putting into operation of an anesthetic evaporator, which could not be acceptable for the user, and it would require the presence of a measuring instrument. In addition, gas and anesthetic would be lost during rinsing.
U.S. Pat. No. 4,444,182 made a suggestion for avoiding the disadvantageous consequences of the oblique position of the anesthetic evaporator, and especially those of the upside down position of the anesthetic evaporatdr, in which the anesthetic reserve is no longer at the bottom, but flows at the level of the gas inlet. In this prior-art anesthetic evaporator, a plurality of gas-carrying channels, which immerse into the anesthetic liquid and are closed by it, are provided in the standard operating position, i.e., when the evaporation chamber forms the bottom of the anesthetic evaporator. If the anesthetic evaporator is tilted, or even turned upside down, the openings of one or all of the channels are exposed, so that the gas can flow via these exposed channels.